This invention relates to electrochemical batteries.
There are tough requirements on electrochemical power sources for tractionary applications like electric trucks and cars. The power and energy density should be high, and the system must be simple and reliable and easy to service. Furthermore, first cost must be low and the cycle life in tough and varying operation, should be at least so long that the capital costs turn out to be about the same level as the operating costs, which should be dominated by the cost for the electrical energy. The efficiency in the energy conversion will also be of great importance for the kind of power sources which satisfy the economic requirements indicated above.
The lead acid battery is the power source which today is close to satisfying the requirements mentioned above, but it is nevertheless unsatisfactory because of too low energy density. In practice, it is possible to extract 20 W/kg of a tractionary lead acid battery during 1 hour which gives an action distance of but 50-100 kilometers for an electric car cruising at about 50 km/h or somewhat above.
A lot of work is, therefore, put into the development of power sources with a higher energy density and satisfactory power density for tractionary applications. Efforts have been made to reach high enough energy densities that the electric vehicle can be capable of the same performance as a related version with an internal combustion engine. The metal air batteries, the high temperature batteries and the fuel cells are examples of such advanced power sources. These systems are, however, complicated and it has not yet been demonstrated that these systems can satisfy all other requirements which must be put on the tractionary battery, for instance in electric cars. In fact, a lot would be gained with a battery exhibiting the many good properties of the lead acid battery but with doubled energy density, which in the high power region should correspond to the level 40 W/kg during a 2 hour discharge or slightly above that. Such a battery would give twice the action distance for today's electric vehicles during otherwise unchanged conditions. Alternatively, one could maintain the performance of the present electric vehicle but reduce the battery weight with about 50% which would allow much more pay load, of great importance for the electric distribution vehicles. The present invention refers to a battery with this kind of performance and which in other respects meets the requirements put on a power source for general tractionary application. This good result is obtained by a combination of cooperating design features and a special design of the electrolyte system which produces a number of important advantages despite the fact that this special feature is in conflict with present practices in the battery technology.
One object of the present invention is thus to provide a battery with at least twice the energy density of the tractionary lead acid batteries presently use in electric cars.
Another object is to provide a battery which exhibits a much better cycle life than deeply tractionary lead acid batteries.
A further object is to provide a battery which uses raw materials which are available in large quantities so that restricted availability of raw materials should not stop the application on a very large scale.
Yet another object is to design the battery in such a manner that the used materials can be easily recovered in order to keep the user's cost down.
Still another purpose is to provide a battery which can take tough treatment with no risk for fire or other hazards.
An additional object is to provide a battery which is sealed against the environment and which requires a minimum of maintenance and service.
One further object is to provide a battery which can be easily manufactured on a large scale and be built in a modular shape for easy assembly and simple adjustment to different kinds of vehicles or other applications.
One additional object is to provide a method for eliminating gas developed in a battery.